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When it comes to running, there’s a gender gap between men and women that even elite training doesn’t erase.

“Why are most women, on average, slower than men?” asks Runner’s World in the April 2015 edition. “At every distance up to the marathon, the gap between men’s and women’s world record times is nine to 10 percent—and it’s a similar or even higher percentage among recreational runners.”

Chris Schwirian, a Biological Sciences lecturer at Ohio University, explains the differences in body composition and function between men and women.

“Faster men’s times for 100 to 800 meters are mostly due to men, on average, having greater muscle mass—and a larger portion of it is fast-twitch, which allows them to generate greater force, speed, and anaerobically produced energy,” Schwirian told Runner’s World. “At all distances beyond 800 meters, the main reason for the gap is men’s higher aerobic capacity [VO2max], on average, which is due to their typically having less body fat, more hemoglobin and muscle mass, and larger hearts and lungs than women.”

Studying the Physiology of Running

“I think it is important to note that women are capable of extraordinary performances; most men couldn’t come anywhere near the 10.49 second 100m record held by Florence Griffith-Joyner or Paula Radcliffe’s 2:15:25 Marathon record,” Schwirian says, providing additional information for the A&S Forum.

Chris Schwirian

He’s taught courses in human and exercise physiology at Ohio University since 1996 and has been involved in the physiological testing of athletes since he was an undergraduate Biological Sciences student at Ohio University. “Over the years, I have tested runners, cyclists, swimmers, and rowers at almost every level of competition from high school and college to Olympic athletes (rowers).”

Schwirian describes himself as a “pretty good runner” in high school (co-captain of cross country at Newton North High School in Massachusetts) and a “mediocre walk-on college athlete.” He ran track (800m) and cross country at Ohio University, earning a B.S. in Pre-Exercise Physiology from the College of Arts & Sciences in 1994. He also earned an M.S. in Physical Education from the College of Health Science and Professions in 1995.

He’s still running. He recently competed in USA Triathlon’s Olympic Distance age group nationals in Milwaukee.

“I did OK,” he says. “I came in 88th out of about 220 in my age group, and I hope to improve on that next year.”

Average Gender Gap for Marathons: 20-22 Percent

For most running events the so-called gender gap for world record performances is approximately 10 percent. There was a time when women’s improvements in long distance events were greater than men’s improvement and there was speculation that women might overtake men in longer running events. “This appears to be more related to sociology than biology; there has been a large increase in participation in endurance events by women over the past several decades,” Schwirian says.

Women could not participate in running events longer than 800m in the Olympics until 1960, and the first Olympic marathon for women wasn’t until 1984.

“More recent analyses suggest that this gender gap has been stable for past few decades, although it is not necessarily stable across all age groups,” he says. The gender gap for world record performances is around 10 percent for running events between 200m and 10km distances, and is slightly smaller for the 100m and marathon (currently 9 percent) based on IAAF world record times. The average gender gap, however is closer to 20-22 percent for half marathon, marathon, and ultramarathon (e.g. 100km and 161km) events. For 24-hour ultramarathon performances, the gender gap is approximately 13 percent for the top finishers and the average of the top 10 finishers.

There is a tendency for the gender gap in marathon pace to become greater as a function of age. This difference, however, appears to be mostly due to a relative decrease in female participation as age advances rather than a biological difference, Schwirian explains.

The Sprint Performance Gap

Peak sprint performance is influenced especially by muscular power (related to both strength and velocity), and for longer sprints, the ability to generate energy anaerobically. Men are generally able to generate greater peak powers mostly due to their larger muscle mass. Men and women have a similar number of muscle fibers, but the higher testosterone levels in men results in larger size muscle fibers.

Men and women tend to, on average, have similar fiber type proportions, but in men, the fast twitch fibers tend to be larger than the slow fibers and in women, the slow twitch fibers tend to be the largest. Why does this matter?

“Well, this means a greater proportion of a man’s muscle mass is fast twitch and a greater proportion of a woman’s muscle mass is slow twitch. This contributes to the ability of men to generate force very rapidly relative to women, which facilitates greater power and peak running speeds. Additionally, the large muscle mass coupled with the high proportion of fast twitch muscle tissue means that men have greater potential to use anaerobic metabolism; they are better equipped to generate energy rapidly during sprint events. This would be especially important in races between 200m and 800m,” Schwirian says.

The Endurance Gap

The principal determinants of endurance performance are aerobic capacity (also called VO2max), the anaerobic (or lactate) threshold, and running economy. An athlete’s aerobic capacity is his or her maximal ability to take up and use oxygen. The anaerobic threshold is an important predictor of what percentage of maximum an athlete can maintain during long distance exercise.

“Finally,” he says, “running economy is an indicator of efficiency. It is the amount of oxygen consumed per distance. In this way, running economy is a little bit like your car’s fuel economy. If the car (or athlete) is more efficient, the car (or athlete) will require less energy (and less oxygen) for a given speed or distance.

“For any different level of training, men and women tend to have similar values for anaerobic threshold and running economy. Thus, the main reason for the gender gap in longer races is due to differences in aerobic capacity (VO2max).”

Men tend to have significantly higher values for VO2max, the maximum rate at which one can take up and utilize oxygen. Men can consume approximately 40 percent more oxygen than women when it is reported in liters of oxygen per minute. In these terms, a large part of the difference is because men are larger and more oxygen is needed to support a larger organism. The gender difference for VO2max becomes a bit smaller (20 percent) if one scales it relative to body mass (in milliliters of oxygen consumed per kg body mass per minute), but the fact that there is still a difference suggests that this is not all about body size.

“Part of the difference that still exists is due to the fact that men have, on average, a lower percent body fat and are thus, on average, leaner, and lean tissue consumes more oxygen than fat tissue. The gender difference in VO2max shrinks further (to 15 percent) if you scale it relative to lean body mass, suggesting there is still a real biological difference between men and women that is not simply explained by size or muscle mass,” Schwirian says. “This difference in VO2max can be explained by the fact that men tend to have a higher concentration of hemoglobin for transporting oxygen in the blood, larger hearts for pumping oxygen rich blood to the working muscles, and larger lungs for oxygenating the blood.

The Fat-Burning Gap?

At any given intensity, women tend to burn more fat than men. On the surface, this would seem to favor women during endurance events. If they are able to rely more on fats, then they are able to better preserve their glycogen stores, and thus delay the onset of fatigue. This would especially be true of events lasting more than two hours. However, during long distance events lasting more than two hours, most athletes would consume some carbohydrates, thus negating this potential performance benefit.

On the other hand, while both men and women are able to glycogen load to some extent, there are some reports that suggest men are able to maximize glycogen stores to a greater extent than women during typical glycogen-loading protocols, he says.

“Interestingly the gender gap for swim performances between distances of 50m and 1500m gets progressively smaller as distance increases. It has been suggested that this differences is due to females’ relatively greater efficiency during swimming. This efficiency, in turn, is thought to be due to less drag (smaller, more streamlined bodies) and perhaps greater buoyancy (greater percent body fat) in women,” Schwirian says.

Amongst elite ironman triathletes, the average gender gap is smallest for the swim (12 percent), followed by cycling (15 percent), and greatest for running (18 percent).

“It should be noted that these gender gap values seem a bit higher, in part because they are the average gender gap, whereas many studies present the gender gap as the difference between the top male and top female athlete for a given event,” he adds.

“It appears then, that the gender gap is greater among the athletes who finish last than among those who finish first.”